The present invention relates to a synthetic resin fastener used to attach tags and labels indicating the price and quality to merchandise, seal the covers of instruments or meters, connect together a pair of slippers and sandals, and close the mouth of bags.
Many patent applications have been filed regarding such fasteners, and the U.S. Pat. No. 4,240,183 may be cited as an example.
The fastener 11 disclosed in the above U.S. patent, as shown in FIGS. 1 and 2, consists of a filament 12, a socket 14 secured to one end of the filament 12, and a head 13 secured to the other end of the filament 12. Such fasteners must be very small because the smaller and the less conspicuous the fasteners, the more easily and clearly the tags and labels can be seen. The fastener shown in FIGS. 1 and 2 has the following dimensions: ##EQU1##
As shown in FIG. 3, the head 13 is inserted into an insertion hole 15 of the socket 14 and passed through an insertion wall 17 of an annular flange 16 formed in the insertion hole 15 until it engages with the annular flange 16 as shown in FIG. 4.
The fastener 11 is formed of synthetic resin such as nylon and polypropylene in one piece, so that a large number of fasteners with the same quality can be produced. The fastener 11 is very small and slender and thus easy to attach to merchandise. It is also good in terms of design and therefore, in recent years, consumed in large quantities worldwide.
However, when such fasteners are to be attached to a large number of articles at a time, the following problems arise.
(1) The filament 12 (FIGS. 1 and 2) is stretched to make it fine and stronger after being formed of synthetic resin. After being taken out of the stretching process, the fasteners 11 are packed into bags, for example 1000 pieces a bag with the heads 13 aligned and put on the bottom side of the bag and the sockets 14 on the inlet side.
However, since the head 13 has two engagement projections 18, 18, the fasteners 11 are easily caught by others. Furthermore, some filaments may get slightly curved by moisture absorption after stretching or by distortion during molding, which makes troublesome the work for aligning the individual fasteners that are in disarray when taken out of the stretching process and packing into a bag.
(2) When the fasteners are to be attached to merchandise, a number of fasteners, about 50 pieces, are taken out at one time from a 1000-piece bag. As mentioned above, the fasteners are packed in the bag with the sockets 14 aligned on the inlet side of the bag, but since the engagement projections 18 project from the heads 13, a number of other fasteners get entangled with those being taken out and are also drawn out together with those intended to be taken out.
As a result, a group of fasteners taken out have to be realigned, with the sockets disposed at the top, lowering the tag attaching preparation work efficiency.
(3) From a lump of about 50 fastener taken out of the bag, individual fasteners are picked up one by one for use. As in (2), a socket 14 is picked up by fingers. However, in this case also, the entanglement between the engagement projections of adjacent heads or between the engagement projections and sockets makes it difficult to swiftly pick up the fasteners one by one. As a result the work efficiency is affected adversely.
(4) As shown in FIG. 4, the engagement projection 18 has a sharp edge at the end, so that the engagement projections 18 can securely be locked with the annular flange 16 that has annular engagement surfaces 16a and 16b at its top and bottom. The sharp edges of the engagement projections 18, however, may injure the fingers of the operator.
(5) The engagement projections 18 will easily catch and damage fiber products.
(6) As mentioned above, the fasteners should be as small and fine as possible. However, the head 13, as described above, has elastic engagement projections 18 protruding from the rear end thereof, so that structurally the projections 18 must bear the engagement force between the head 13 and the socket 14. This means that the head 13 can hardly be further reduced in size. The socket 14 into which the head 13 is inserted has also little chance of being reduced in size.
(7) When the head 13 is passed through the annular wall 17 of the annular flange 16 formed in the insertion hole 15 of the socket 14, the engagement projections 18 that are normally flared open are closed or settled onto the neck 19 while being inserted. Therefore, the finer the neck 19, the easier it will be to fold the flared engagement projections 18 to provide a smaller distance between the tips of the projections.
However, since the neck 19 is not subjected to the stretching process, it is significantly fragile compared to the filament 12 that were reinforced by stretching. Therefore, reducing the diameter of the neck 19 will result in reduction in the strength of the head 13.
On the other hand, since the engagement projection 18 is a part that bears the tension that acts on the filament, i.e., the engagement force between the head 13 and the socket 14, the engagement projection 18 cannot be made thinner.
(8) While thickening the neck 19 will increase the strength of the head 13, it renders difficult the folding of the flared engagement projections 18, increasing the resistance against the head and the projections passing through the annular wall 17.
(9) When the engagement projections 18 are formed larger, the engagement force will increase. However, it also increases the resistance against the projections passing through the annular wall 17 of the annular flange 16. Making the engagement projections 18 smaller will render the passage through the annular wall 17 easy, but reduce the engagement force.
(10) Molding of the engagement projections 18 requires a mold with high precision, the manufacturing of which is costly.